Abstract

Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.

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Acknowledgments

This study was supported by the following projects: WTZ “Wissenschaftlich Technische Zusammenarbeit” (ES 08/2008) of the Austrian Agency for International Cooperation in Education and Research, Spanish Acciones Integradas (HU-2007-11), BOKU Doc Grants 2008, and Spanish projects CGL2006-06596/BTE and CSD2006-00041 (R&D Plan MICINN and FEDER Founds, Spain). We would like to thank Friedrich Zott and Barbara Mayer from the Institute of Mountain Risk Engineering (BOKU, Vienna) for their invaluable work installing and maintaining the monitoring station at Lattenbach and Illgraben as well as Catherine Berger from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL, Birmensdorf) for her help at Illgraben.

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